jQuery Overview

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    Introduction to jQuery Nate Haug
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    Let's kick things off with a quick overview of a presentation
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    of the basics of jQuery.
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    This presentation will cover the bare minimum
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    that you need to know in order to get
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    started using jQuery with Drupal.
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    We also have another DVD in the Lullabot Learning Series called
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    An Introduction to jQuery that covers each of these concepts
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    more in depth.
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    Let's get started.
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    First of all, what is jQuery?
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    jQuery itself stands for JavaScript Query,
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    which we'll see where the query comes into things
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    later in this presentation.
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    It's a JavaScript library smaller than most images on the page.
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    Compressed, it's only about 23k, more or less,
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    depending on which version of jQuery you're actually using.
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    Overall though, it significantly reduces the amount of code
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    that you would need to write.
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    As a developer, writing JavaScript code can actually be really
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    tedious and rather confusing.
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    And jQuery simplifies all of it, making it so that all of your code
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    works across all different browsers, which is the next benefit.
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    Any code that you write in jQuery, you can pretty much rest
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    assured that it'll work across all browsers and all platforms
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    without any additional changes.
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    Lastly, jQuery provides a set of visual effects that
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    can add wow factor to your site, such as fading
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    in or sliding up and down.
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    Let's take a look at some jQuery syntaxes.
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    First of all, jQuery only contains one function in the entire library,
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    the dollar sign function.
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    And the dollar sign function can do multiple things
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    depending on the arguments that you pass into it.
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    The first thing, and the most common thing
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    you'll be doing with the dollar sign function is doing selectors.
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    Selectors allow you to find elements on the page
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    so then you can operate on them.
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    If you pass an HTML into the dollar sign function,
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    it will automatically create Dom objects that you can then place
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    on to the page, wherever you like.
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    And lastly, the dollar sign also provides a set of detection scripts
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    that allow you to determine which version of browser
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    you're currently working with.
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    And even though this isn't really necessary within jQuery most
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    of the time, you can now use the dollar sign function to check
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    information about the browser.
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    In later versions of jQuery we're now
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    no longer using the browser property,
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    though it's still available.
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    Instead, we're checking the support.
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    This support object will tell you information about the browser,
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    such as whether or not it properly renders the box model
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    or supports opacity, making it so you
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    can fine-tune your scripts to provide
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    a good experience for all users.
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    So let's talk a little bit about jQuery selectors.
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    jQuery selectors allow you to find an element on the page
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    so that you can operate on it.
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    Selectors are one of the main reasons why the jQuery library
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    became so popular to begin with.
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    First of all, you can pretty much use any of your existing knowledge
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    about CSS and reapply it to jQuery.
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    So, for example, you can find an element by class,
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    simply by using a dot in front of the name of the class,
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    just like in CSS.
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    You can also use the hash symbol, just like CSS,
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    to find an element by its ID.
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    Or, if you want to, you can even select multiple elements
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    by separating them with a comma.
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    You can even use advanced CSS selectors as provided
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    by the CSS 3 specification.
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    Even if the user's browser doesn't yet support CSS 3,
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    jQuery provides the functionality to make
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    it so that you can use CSS 3 advanced selectors
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    across all browsers.
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    In this particular example, we've made it so that we can select
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    an element by its attribute.
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    So for example, this particular selector
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    will find all text fields on a page by checking its attribute
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    type is equal to text.
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    You can even do more advanced selectors, such as this attribute
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    selector that will find all images on the page that end with a ping.
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    So basically, finding all ping images on the page.
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    It's important to note that this attribute selector is probably one
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    of the biggest differences in the jQuery API between older
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    versions and the newer ones.
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    The first version of jQuery ever included in Drupal was in Drupal 5
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    and it was jQuery 1.0.4.
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    Later versions of Drupal then included newer versions of jQuery.
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    Drupal 6 included jQuery 1.2 and newer versions of jQuery
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    can be added to Drupal core by using the jQuery update module.
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    Drupal 7 includes the latest release as of now of jQuery, jQuery 1.4.
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    So just keep in mind that if you're using older versions of jQuery,
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    you'll need to include this @ sign in your attribute selectors.
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    All newer versions of jQuery, that @ sign can now be omitted.
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    So once you've found an element on the page using the jQuery selector,
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    you'll likely want to do something with it.
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    Most commonly, you'll apply an effect to that element
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    that you have selected.
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    jQuery provides a set of effects, the most
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    common of which, or basic of which, is called hide,
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    and its complement, show.
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    This will simply immediately take an element that is visible on the page
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    and hide it immediately.
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    Interestingly though, the hide effect,
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    though being the most simple effect that jQuery provides,
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    is also one of the most extravagant.
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    If you add a parameter to the hide method,
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    then it will in fact make an effect that's pretty exciting.
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    This is the way it looks, taking an element and slowly hiding it.
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    We'll collapse it to the left and to the top,
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    and fade it out at the same time.
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    Besides just using slow, and its complement, fast, you can
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    also pass in a particular integer.
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    If you pass an integer value, jQuery will interpret
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    that as the number of milliseconds that that effect
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    will take to complete.
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    So, for example, 3,000 would take 3 seconds
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    to complete a particular event.
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    So besides just hide and show, you can also
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    use some effects such as fade out.
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    And fade out will simply fade out the element.
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    It also has a complement, fade in.
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    And this is the way that these effects look.
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    Lastly, besides hide, show, fade out, and fade in,
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    there's also slide up, and its complement, slide down.
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    And this is the way that this effect looks.
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    And that's a general summary of the effects
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    that are available within jQuery.
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    Besides these effects, there's also some very useful toggle commands
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    that you can use that do the opposite, whether or not
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    an element is shown or hidden.
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    So, for example, if an element is currently slid up and hidden,
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    then you can use slide toggle, and it will slide down.
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    If it's already down, then it will slide the complement, back up.
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    There's also some great effects that you can use by toggling classes.
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    Toggling classes will essentially add
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    or remove a class based on whether or not
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    that element currently has it.
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    So, for example, you could toggle a class, such as hover to make it
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    so that an element is hovered when the mouse is over it,
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    and then remove the class hover when the mouse is moved back out.
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    Class manipulations are great, because they make it so that you
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    can apply all of the powers of CSS simply by toggling
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    on or off a particular class.
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    One of jQuery's greatest features is its ability to chain
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    together separate requests.
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    It's also where the word query comes into the word jQuery.
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    So, for example, let's take an h1 element, which we've selected here
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    on the first line of this code.
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    And then we've pre-pended the word hello,
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    and then appended an exclamation mark, making it
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    so that the word hello now surrounds this h1 with an exclamation
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    mark at the end.
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    And then we can fade it out and fade it in.
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    Each one of these actions will take place in sequence.
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    So that first the pre-pend will happen, then the append, then
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    the fade out, then the fade in.
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    And you can chain together these commands endlessly,
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    all of these effects actually taking place on the original element that
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    was selected.
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    Chainability was a great innovation introduced in the jQuery library.
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    So once you've found an element on the page,
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    and once you're able to actually do some effects on it,
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    you'll probably want those effects to actually take
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    place based on the user action.
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    These 3 steps put together the basics
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    of just about all jQuery scripts.
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    So a jQuery event allows you to actually trigger this action
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    in response to the user clicking, or hovering, or doing
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    some other action on the page.
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    These are the most common events used within jQuery.
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    So click, obviously, makes an element react to a user clicking.
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    Changes responds to any change within a select list,
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    or radio button, or checkbox.
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    Toggle is very similar to click, only it will
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    execute these actions alternatingly.
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    Hover, very similarly, will respond to rolling the mouse over something
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    and then rolling it back out.
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    Each one of these events all take a function name as their arguments.
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    This function name is what will actually be executed when the user
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    does this particular action, whether clicking,
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    or changing a form element, or hovering
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    the mouse over a particular item.
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    Besides adding events, you can also remove
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    events that you've previously bound by using the unbind method.
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    So that does it for basic coverage of the jQuery concepts.
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    First of all, there's only one function within the jQuery library,
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    the dollar sign function.
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    With this dollar sign function, most commonly
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    you'll be selecting an element on the page using a selector.
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    Once you've found that element, you'll apply an effect to it.
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    Together, selectors and effects aren't that much use,
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    unless you're actually doing them in response
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    to a user's action on the page, for which we use jQuery's events.
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    And lastly, all of jQuery's abilities
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    are completely chainable, making it so you can put together
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    a long sequence of events simply by concatenating them
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    all on top of the same selector.
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    So this covers the fundamentals of the jQuery library.
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    We'll be doing some more hands-on examples throughout this video,
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    but for a more in-depth coverage of all of these features
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    within the jQuery library, check out the Lullabot Learning Series
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    DVD, An Introduction to jQuery.
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    Let's go write some code.

Jquery Overview

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Provides a high-level overview of jQuery to people who are brand new to this JavaScript library.

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